As part of a study about the prevalence of intestinal parasites, physicians and/or epidemiologists need to collect stool specimens.  Among the following choices, which describes a procedure that will allow optimal microscopic detection of parasites?

(a) Patient collects a specimen at home in a cup, and brings it to a lab within 48 hours.
(b) Patient collects a specimen in a tube containing 10% formalin and brings it to the lab when it is convenient.
(c) Patient collects a specimen in a tube containing PVA and brings it to the lab when it is convenient.
(d) Patient collects a specimen and immediately places a portion both in 10% formalin and in PVA.